Chemical+Bonding


 * Section 8.1 Forming Chemical Bonds**
 * Section 8.2 The Formation and Nature of Ionic Bonds**
 * Section 8.3 Names and Formulas for Ionic Compounds**
 * Section 8.4 Metallic Bonds and Properties of Metals**
 * Section 9.1 The Covalent Bond**
 * Section 9.2 Naming Molecules**
 * Section 9.3 Molecular Structures**
 * Section 9.4 Molecular Shape (honors only)**
 * Section 9.5 Electronegativity and Polarity**


 * Essential Questions**

A neutral atom has the same number of positive protons and negative electrons. The electrons are configured in pairs found in the sublevels (s, p, d, f) of the main energy levels (1-7). When electrons are paired within orbitals, they will have opposite spins.
 * What is the orbital configuration of a neutral atom?**

The outermost energy level of an atom is its valence shell, and electrons located in the valence shell are called valence electrons. The number of valence electrons determines the atom's ability to gain, lose, or share electrons to combine with other atoms and form compounds. Atoms gain, lose, or share valence electrons in order to achieve a stable noble gas configuration with a full outer energy level. Generally, the number of single electrons in the valence shell determines the number of bonds an atom will make.
 * How does an atom's electron configuration affect its chemical properties?**

Elements become more stable by bonding. Elements that have 8 valence electrons are more stable. Metals have 3 or fewer valence electrons and lose electrons to nonmetals which have 5 or more valence electrons. This transfer of electrons is known as ionic bonding. For example, calcium has 2 valence electrons and chlorine has 7 valence electrons. Calcium needs 2 chlorine atoms to transfer the electrons to. So the compound CaCl2 is formed. All compounds are neutral so notice that the charges: +2-1-1=0. Nonmetals bond by sharing electrons. For example: water H20.
 * What is chemical bonding?**


 * How does chemical bonding affect a compound's properties?**
 * Solubility:** The opposite charges of ions in an ionic compound leads to the formation of an ionic bond and when many positive and negative ions attract each other, a salt crystal is formed ("salt" refers to any ionic compound). Since water is a polar molecule, having areas of negative and positive charges, these are attracted to the positive and negative ions of a salt. When the attraction between the water molecules and the ions becomes stronger than the attraction between the ions themselves, the salt dissolves. On the other hand, sugar is a polar molecule held together by covalent bonds and has positive and negative areas like water molecules. Sugar molecules arrange themselves so that the positive areas of one molecule are attracted to the negative areas of the water molecules. When the attraction between water and sugar overcome the attraction between sugar molecules themselves, the sugar dissolves. The textbook has an incredible animation of this very property using NaCl vs CH3OH on p. 490, Figure 10 - click the "Concepts in Motion" button.

Other resources: http://www.chem.wisc.edu http://student.ccbcmd.edu


 * Hardness or Brittleness:** The strength of an ionic bond is a result of the attraction between oppositely charged ions and when a strong enough force pushes the ions out of alignment, forces of repulsion created by nearby like-charged ions break the crystal apart. Although there are positive and negative areas around covalently bonded compounds, when a force is applied to these compounds, molecules, rather than individual ions, are broken apart from each other. How strong the intermolecular force is determines whether the covalent compound is hard or soft. In metals, cations are pushed around in the sea of electrons and so the metal simply bends (or dents). Se p. 212-215 of the textbook - it describes and has diagrams of ionic crystals. For information on covalent solids, see p. 270. For information on metallic solids, see p. 225-6.


 * How do I name covalent molecules?**

mono - 1 di - 2 tri - 3 tetra - 4 penta - t hexa - 6 hepta - 7 octa - 8 nona - 9 deca - 10
 * Prefixes** tell how many of each atom are in the molecule:

Examples: NO nitrogen monoxide NO2 nitrogen dioxide N2O dinitrogen monoxide N2O5 dinitrogen pentoxide

1. Write the element which appears to the __**left and lower** **FIRST**__ (add prefix if more than one) 2. Write the next element and __**change the ending**__ to -**ide** (drop the "o & a" from prefix before a vowel) 3. Use prefixes to tell __**how many of each kind of atom**__ are in the molecule
 * Naming compounds**:


 * How do I write the Name of an Ionic Compound?**

1. The name of an ionic compound has two parts. 2. The cation is named first and then the anion. Example: NaCl is sodium chloride. 3. Most cations have the same name as their element. Examples: sodium, potassium, magnesium, gold, silver, etc. 4. The root name of anions composed of a single atom are found on the periodic table. 5. These anions change the last part of the original element's name to the suffix - ide. Example: F flourine and the ion F-, is fluoride.


 * How do I Write the Formula for an Ionic Compound?**
 * Follow a simple rule: The electrical charge must equal zero!!!
 * The correct formula contains the fewest positive and negative ions that are needed to make the total electrical charge zero. For example, the formula for potassium fluoride is KF.
 * If more than one ion is needed to reach zero charge, subscripts are used to indicate more than one of that ion. Example: CaCl2 is calcium chloride.
 * Use the criss-cross method of determining these subscripts.
 * Move the number of the charge on the ion down to the subscript of the opposite ion.
 * Reminder for criss-cross method: Don't use criss-cross when the positive and negative charges add up to zero. Example: CaO = correct formula, Ca2O2 = incorrect formula. Reduce subscripts!!!